We propose to examine the mechanisms of retinal degeneration associated with specific mutations in the human rhodopsin gene: the first in codon 23, a substitution of histidine for proline at position 23 of rhodopsin (P23H) and the second in codon 347, a substitution of serine for proline at position 347 (P347S). These two forms of the mutant human rhodopsin gene have been used to generate separate lines of transgenic mice. All five of the P23H and P347S transgenic lines represent models for human autosomal dominant retinitis pigmentosa because the transgenic retinas express mutant opsin protein and undergo photoreceptor degeneration with reduced and delayed ERGs. The studies proposed here are designed to define the mechanisms of photoreceptor loss in both the P23H and P347S transgenic retinas. Specifically, we will: 1) determine the intracellular fate of the mutant rhodopsins, 2) define the properties of P23H and P347S rhodopsin expressed within a transgenic retina, 3) quantitate the amounts of transgenic opsin present within the photoreceptors across the timespan of the degeneration, 4) define the developmental time course of mutant opsin expression, 5) determine the rate of outer segment disk addition in the transgenic retinas, and 6) evaluate the levels of specific nucleotides, particularly cyclic guanosine monophosphate, over the time course of degeneration. Potential treatments that might improve or prolong photoreceptor survival in the transgenic retinas will be tested using a recently developed co-culture system. Photoreceptor survival will be measured in transgenic retinas co-cultured with retinal pigment epithelial cells in the presence or absence of factors that might modify the effects of specific defects in rhodopsin. Definition of pathogenetic mechanisms and studies in the transgenic co-culture system may provide rational bases for designing treatments applicable to human patients with rhodopsin mutations.